A suspension bridge is a bridge that is supported by cable suspenders hanging from main catenary cables that are strung from one pier to the next. This type of bridge has been constructed commonly for long spans of the order of 5,000 feet. Longer spans up to 6,500 feet have been constructed in recent years, and spans of 10,000 feet have been planned. However, span length increases of conventional suspension bridges are subject to a serious material limitation, i.e. the reduction of the carrying capacity/weight ratio of the catenary cables (C/W ratio for short) occurring with the increase of span length. For example, a suspension bridge with a C/W ratio of three means that for this bridge, every pound of steel in the catenary cables will carry three pounds of bridge load in addition to its own weight. A suspension bridge with a main span of 5,000 feet, usually has a C/W ratio of around 5 or 6.
As the bridge increases in span length, the C/W ratio will decrease at a rate depending on the geometry, material strength, etc. At a span length of 16,000 feet, for example, the C/W ratio would drop to about 1:1, meaning a carrying capacity of only one pound for every pound of steel used in the catenary cables. This will not only place a limit on how long a suspension bridge can be, it will also result in a very inefficient and uneconomic design.
The invention herein disclosed enables the span length of a suspension bridge to be increased substantially without reducing the carrying capacity of the catenary cables. For example, a 16,000-foot bridge span as cited above, when utilizing the present invention, will maintain a carrying capacity of the catenary cables at a C/W ratio of 3 or 4, as if the bridge span is only 10,000 feet long. The practical limit of suspension bridge spans will thus be raised from about 16,000 feet using prior art principles to 22,000 feet.